The invention relates to a device for inhaling a powdery, micronized, pharmacologically active drug, which has been converted into a flowable formulation, having a supply container for the drug formulation, which supply container is completely or partially closed off at its lower end by a rotatable or displaceable, manually actuated metering plate for the repeated reception and delivery of a predetermined, reproducible quantity of the drug from the container. The drug formulation can consist of pure micronized active substance (e.g. soft pellets) or of a mixture with a pharmaceutically acceptable carrier (e.g. lactose monohydrate). Additionally, the device has a mouthpiece for inhaling, a dispersing chamber being connected upstream of said mouthpiece.
During inhalation, the metered drug is dispersed inside the inhaler into largely respirable particles of the active substance. It has been shown that numerous drugs can advantageously be administered into the lung as an aerosol. As a result, in many cases a particularly rapid effect of the drug is possible whilst maintaining a dose of the active substance which is very low and, at the same time, causes little stress to the patient.
Up to now, numerous apparatuses for administering an aerosol have been developed. For example, dissolved drugs can be nebulized so finely by means of compressed-air or ultrasonic nebulizers that the resultant aerosol is respirable. A disadvantage is the considerable energy requirement for these apparatuses for nebulizing the solutions into respirable droplets, which results in large apparatuses and means dependence on external energy sources (e.g. mains electricity, accumulators). Also, many drugs cannot be formulated as a stable aqueous solution.
Another way of administering active substances into the lung consists in dissolving or dispersing the active substance in a pressure-liquefied propellant. When this solution or dispersion is released by means of a metering system, the active substance is provided in a very fine form by the sudden evaporation of the propellant and can be inhaled.
These systems harbour a plurality of disadvantages, for example:
very many patients do not manage the required coordination between triggering of the puff discharge and the inhalation;
contribution to environmental pollution by propellant gases;
the patients are irritated by the cold shock due to evaporating propellant;
the high speed of the aerosol leads to appreciable quantities settling in the throat area and can favour side effects there;
in total, only small doses of active substance (about 1 to 2 mg) can be administered.
In order to overcome the disadvantages of the compressed-gas aerosols, a plurality of powder inhalers were developed, in which the inhalation air of the patient is used for dispersing the drug formulation. This dispenses with the coordination of breathing and triggering the dose which is difficult for the patient to manage.
An example of a commercially available powder inhaler is specified in the British Patents 1,122,284 and 1,331,216. This apparatus is loaded with hard gelatine capsules in which the active substance is situated in a micronized form. When the capsule has been opened by two needles, the capsule is set in rotation by the flow of respiratory air during inhalation, as a result of which the micronized active substance is dispersed into the air flow and passes via the inhalation air into the lungs of the patient.
The previously known powder inhalers still show disadvantages:
they have to be loaded and cleaned in a laborious manner;
generally several inhalations are required in order to empty the capsule completely;
patients can unintentionally breathe into the device, as a result of which moisture is precipitated therein, which has a very adverse effect on the metering precision and dispersion of subsequent doses of active substance;
some devices show a high resistance to breathing, which causes additional stress to the patients. Other devices require very high inspiratory flow rates in order to achieve satisfactory dispersion, which is achieved only to an insufficient extent, particularly by small children and older patients.
An example of a powder inhaler with multiple doses is described in EP 0,237,507 and in EP 0,069,715. In these cases, the active ingredient is moved from a reservoir via a perforated membrane into a flow channel and dispersed with the inhalation air of the patient. However, even this device has disadvantages:
dependence of the metering precision on the inhalation flow. In small inhalation flows, cases of incorrect metering and lack of metering were observed, which causes problems since the patient has no control over the delivery of the active substance due to the small quantities of active substance administered;
dependence of dispersion on the inhalation flow;
in this case, as also in the abovementioned single-dose devices, patients can unintentionally breathe into the device, as a result of which moisture is precipitated therein, which has a very adverse effect on the metering and dispersion of subsequent doses of active substance.